There are many types of railroad construction equipment that comprise a mobile platform that is able to travel on and off railroad tracks, including excavators, commonly used to dig the trenching for new railroad tracks, perform railroad maintenance, clear brush below roadbed level, and clean culverts around railroad tracks.
Excavators with hydraulic drive systems are widely used in the related art relating to railroad construction. The two main sections of an excavator are the house and the undercarriage. With referenced to FIG. 1, the house of a mobile platform 100, such as an excavator is the rotating platform 1 that includes the operator cab 2, counterweight 3, boom 4, stick 5, and bucket 6, as well as the engine, fuel, and hydraulic oil tanks. The house attaches to the undercarriage 9 (FIG. 2) by way of a swivel bearing 10. High pressure oil is supplied to the tracks' hydraulic motors (such hydraulic transfer of pressure also interchangeably being referred to herein as “hydraulically communicating” or components being “hydraulically coupled”) through the swivel bearing at its axis, allowing the machine to slew 360 degrees unhindered. As shown in FIG. 1, the undercarriage 9 is equipped with a pair of tracks or wheels 7, which include grousers and may include pads 8. All movement and functions of a hydraulic excavator are accomplished through the use of hydraulic fluid via use of hydraulic cylinders and hydraulic motors.
The engine in a standard hydraulic excavator, for example, serves to drive the hydraulic pumps. Generally, a hydraulic excavator comprises two variable displacement pumps that supply oil at high pressure to the arms, swing motor, track motors, and accessories.
An excavator is a very useful tool in the railroad industry, but many railroad systems extend out into remote locations that make railroad maintenance and repair difficult, since transporting railroad construction equipment, such as an excavator, to remote locations often proves challenging and costly. The process for related art railroad maintenance, for example, typically includes trucking an excavator to a rail site, hoisting and bolting it onto a rail car, and then pulling the rail car with the loaded excavator by locomotive to the site(s) being maintained.
Such related art railroad maintenance processes may be replaced with other related art solutions, wherein the excavator itself incorporates a platform that allows it to travel directly on the railroad tracks, commonly referred to as a “high rail” platform, as shown in FIG. 3. Such a platform typically comprises steel rail wheels used on traditional rail cars, which are attached to the frame of the excavator so that such excavator is able to travel on railroad tracks.
One example related art high rail platform comprises two sets of rail wheels, with each set having a mechanism to raise and lower the rail wheels onto the railroad tracks. One set of wheels is inserted between the leading edge of the tracks of the excavator adjacent to the tracks and the other set is inserted between the trailing edge of the tracks. When both sets of rail wheels are engaged on the railroad tracks, the excavator tracks are elevated from the ground so that excavator is able to ride upon the railroad tracks using the rail wheels. When both sets of rail wheels are disengaged, the excavator tracks are in contact with the ground, thereby allowing the excavator to move about.
However, there are mobility and safety problems with using such high rail platforms of the related art, because for example, when the rail wheels are engaged on the track, the house rises beyond the excavator's normal center of gravity, rendering it somewhat unstable and with a tendency for derailment.
Recent improvements to the high rail system include a “high and wide” platform allowing improved clearance and stability. Such a platform is a purpose-built undercarriage that is heavier and wider than the original factory excavator undercarriage, causing the balance of weight to shift and the center of gravity to lower, thereby making the excavator considerably more stable on the rail lines. With reference to FIG. 4, a platform 14 of such related art systems generally embodies a drive arm assembly 15 that contains a motor drive assembly, which is attached at each end of the platform, wherein rail wheels 16 are mounted and hydraulically powered and controlled. As shown in FIG. 5, the drive arm assembly comprises rail wheels 16, drive box 17, lid 18, drive arms 19, and a hydraulic motor drive assembly 20.
Among the problems that have emerged when using hydraulically powered rail wheels are those particularly involving hydraulic pumps and motors that run independently of each other. In reference to the above hydraulic implementation, typically, the hydraulic pump of a standard excavator pulls hydraulic fluid from the reservoir and pushes hydraulic fluid throughout the machine through hose lines and into the rail motor drive, thereby causing the rail wheels to rotate. The rail motor drive then pushes the hydraulic fluid back out into the reservoir. However, failure occurs when the rail wheels rotate independently from the hydraulic pump system, causing the rail motor drive to behave like a pump, pulling into itself hydraulic fluid from the hose lines, while simultaneously pushing hydraulic fluid back into the machine, causing extreme pressure and compromising the hydraulic system.
In view of the above, aspects of the present disclosure provide improvements to the motor drive assembly that overcome the above problems of the related art, as well as others, and provide additional features that will be apparent from the description provided herein.